Capturing circulating tumor cells (CTCs) from the peripheral blood of cancer patients, where they are disseminated among billions of other blood cells, is one of the most daunting challenge. We report OncoDiscover®, a multicomponent nano-system consisting of iron oxide (Fe3O4) nanoparticles (NPs), polyamidoamine generation 4 dendrimers (PAMAM-G4-NH2), graphene oxide (GO) sheets and an anti-epithelial cell adhesion molecule (anti-EpCAM) antibody (Fe-GSH-PAMAM-GO-EpCAM) for the selective and precise capture of CTCs. We further evaluated this system for therapeutically important oncotargets, exemplifying overexpression of the programmed death ligand 1 (PD-L1) as a functional assay on CTCs in cancer patients. We retrospectively evaluated 134 cancer patients for the presence of CTCs and 113 (84%) showed the presence of CTCs. About 62 (55%) of the CTC +ve patients showed CTCs with PD-L1 expression. The personalized cancer detection demonstrated by the OncoDiscover® CTC analysis tool is highly relevant for cancer monitoring and treatment outcomes.